Anti-fouling compositions with a fluorinated alkyl- or alkoxy-containing polymer or oligomer

ABSTRACT

An anti-fouling composition which comprises a cured or cross-linked polymer free of perfluoropolyether moieties and a fluid fluorinated alkyl- or alkoxy-containing polymer or oligomer. Preferably, the fluorinated alkyl- or alkoxy-containing polymer or oligomer comprises a repeating unit of the general formula:  
     —{[CFR—(CFR) m —(O) n ] p —[CFR—O] q }— 
     wherein n is 0 or 1, m is an integer from 0 to 4, R independently is H, F, Cl, Br, or CF 3 , and the ratio q/p is 0-10, and the fluorine-free polymer is an organosiloxane-containing polymer comprising a repeating unit of the general structure —[SiR 1 R 2 —O]—, wherein R 1  and R 2  are independently hydrogen, alkyl, aryl, aralkyl, or a vinyl group.

[0001] This application claims the benefit of European PatentApplication No. 01201071.6, filed Mar. 21, 2001, and U.S. ProvisionalPatent Application Ser. No. 60/294,028, filed May 29, 2001.

[0002] 1. FIELD OF THE INVENTION

[0003] The invention pertains to an anti-fouling composition whichcomprises a cured or cross-linked polymer free of perfluoropolyethermoieties and a fluid fluorinated alkyl- or alkoxy-containing polymer oroligomer, and to a method for inhibiting fouling in an aquaticenvironment.

[0004] 2. BACKGROUND OF THE INVENTION

[0005] Man-made structures such as boat hulls, buoys, drillingplatforms, dry dock equipment, oil production rigs, and pipes which areimmersed in water are prone to fouling by aquatic organisms such asgreen and brown algae, barnacles, mussels, and the like. Such structuresare commonly of metal, but may also comprise other structural materialssuch as concrete. This fouling is a nuisance on boat hulls, because itincreases frictional resistance during movement through the water, theconsequence being reduced speeds and increased fuel costs. It is anuisance on static structures such as the legs of drilling platforms andoil production rigs, firstly because the resistance of thick layers offouling to waves and currents can cause unpredictable and potentiallydangerous stresses in the structure, and, secondly, because foulingmakes it difficult to inspect the structure for defects such as stresscracking and corrosion. It is a nuisance in pipes such as cooling waterintakes and outlets, because the effective cross-sectional area isreduced by fouling, with the consequence that flow rates are reduced.

[0006] The commercially most successful methods of inhibiting foulinghave involved the use of anti-fouling coatings containing substancestoxic to aquatic life, for example tributyltin chloride or cuprousoxide. Such coatings, however, are being regarded with increasingdisfavour because of the damaging effects such toxins may have ifreleased into the aquatic environment. There is accordingly a need fornon-fouling coatings which do not release markedly toxic materials.

[0007] It has been known for many years, for example as disclosed in GB1,307,001 and U.S. Pat. No. 3,702,778, that silicone rubber coatingsresist fouling by aquatic organisms. It is believed that such coatingspresent a surface to which the organisms cannot easily adhere, and theycan accordingly be called fouling release rather than anti-foulingcoatings. Silicone rubbers and silicone compounds generally have verylow toxicity. The disadvantage of this anti-fouling system when appliedto boat hulls is that although the accumulation of marine organisms isreduced, relatively high vessel speeds are needed to remove all foulingspecies. Thus, in some instances, it has been shown that for effectiverelease from a hull that has been treated with such a polymer, it isnecessary to sail with a speed of at least 14 knots. For this reasonsilicone rubbers have gained limited commercial success and there is aneed for improvement of the anti-fouling and fouling release propertiesof these environmentally benign coatings.

[0008] FR 2 537 985 discloses an anti-fouling coating compositioncomprising a methyl organosiloxane resin, a silicone elastomer,polytetrafluoroethylene, an acrylic binder, and a solvent or diluent.Since polytetrafluoroethylene is solid at room temperature, thisdocument does not describe a coating composition comprising a fluidfluorinated alkyl-containing polymer or oligomer.

[0009] EP 0 903 389 discloses an anti-fouling composition comprising aphotocatalytic oxide, a silicone resin or silica, and a water-repellentfluororesin. Tetrafluoroethylene is mentioned as a preferred hydrophobicfluororesin, and in the examples polytetrafluoroethylene particles havebeen used. This document does not describe a coating compositioncomprising a fluid fluorinated alkyl-containing polymer or oligomer.

SUMMARY OF THE INVENTION

[0010] The present invention provides an anti-fouling composition thatsatisfies the requirements, including low surface energy and suitableelastomeric properties, which further decrease the settlement of foulingorganisms and their adhesion strength. It was found that an anti-foulingcomposition which comprises a cured or cross-linked polymer free ofperfluoropolyether moieties and a fluid fluorinated alkyl- oralkoxy-containing polymer or oligomer has advantageous properties withregard to the known non-biocidal anti-fouling compositions.

DETAILED DESCRIPTION OF THE INVENTION

[0011] Within the framework of the present invention, a fluid materialis defined in conformity with ASTM (1996) D4359-90: Standard Test Methodfor Determining Whether a Material Is a Liquid or a Solid. In this testmethod the material under test is held in a tightly closed can at 38° C.The lid is removed and the can inverted. The flow of the material fromthe can is observed to determine whether it is a solid or a liquid. Amaterial that flows for a total of 50 mm or less within 3 min isconsidered a solid. Otherwise it is considered a liquid.

[0012] Preferably, the fluid fluorinated alkyl- or alkoxy-containingpolymer or oligomer has a viscosity between 5 and 1,500 cSt at 25° C.

[0013] Preferably, the fluid fluorinated alkyl- or alkoxy-containingpolymer or oligomer comprises a repeating unit of the general formula:

—{[CFR—(CFR)_(m)—(O)_(n)]_(p)—[CFR—O]_(q)}—

[0014] wherein n is 0 or 1, m is an integer from 0 to 4, R independentlyis H, F, Cl, Br, or CF₃, and the ratio q/p is 0-10. Preferably, theaverage weight MW is 400-40,000, and more preferably 500-10,000. Mostpreferred are such polymers wherein R is F or CF₃.

[0015] In other preferred anti-fouling compositions the repeating unitis selected from at least one of —8 CF₂—CF₂—CF₂—O]— and—[CF(CF₃)—CF₂—O]—, and more preferably {[O—CF₂—CF₂]_(p)—[O—CF₂]_(q)}—,wherein the ratio q/p is 1.25-2.0.

[0016] The anti-fouling composition of the invention comprises a curedor cross-linked polymer that is free of polyperfluoropolyether moieties.Preferably, this polymer is an organosiloxane-containing polymer. Morepreferably, the organosiloxane-containing polymer comprises a repeatingunit of the general structure —[SiR₁R₂—O]—, wherein R₁ and R₂ areindependently selected from hydrogen, alkyl, aryl, aralkyl, and a vinylgroup. It is particularly preferred that R₁ and R₂ are independentlyselected from methyl and phenyl. Another preferredorganosiloxane-containing polymer is a polymer wherein R₁ and R₂ aremethyl.

[0017] A number of coatings with good anti-fouling performance have beenformulated and tested.

[0018] Binders:

[0019] Suitable binders are for instance condensation curablepolydimethylsiloxanes (di-hydroxy-functional) cross-linked withtetraethyl orthosilicate (dibutyltin dilaurate catalysed).

[0020] A siloxane-acrylic hybrid polymer was also tested as a binder.The binders are free of perfluoropolyether moieties. Preferably, theycontain less than 10 wt.% of fluorine, more preferably less than 1 wt.%.Most preferred are binders that do not contain detectable amounts offluorine at all.

[0021] The most preferred binder is a polymer containing siloxane groupswhich is substantially free of carbon in the backbone, e.g. PDMS(wherein substantially free of carbon means that less than 1 wt.% ofcarbon is present). Other suitable polymers are those as disclosed in WO99/33927, particularly the polymers disclosed on page 12, lines 23-31,viz. an organohydrogen polysiloxane or a polydiorganosiloxane. Thepolysiloxane may, for example, comprise a copolymer of diorganosiloxaneunits with organohydrogen siloxane units and/or with otherdiorganosiloxane units, or a homopolymer of organohydrogen siloxaneunits or of diorganosiloxane units.

[0022] Polysiloxanes that can be cross-linked by a hydrosilylationreaction can also be used. Such polymers are known as “hydridesilicones” and are disclosed, for instance, in EP 874032-A2 on page 3,viz. a polydiorganosiloxane of the formula R′—(SiOR′₂)_(m)—SiR′₃,wherein each R′ independently is a hydrocarbon or fluorinatedhydrocarbon radical, at least two R′ radicals per molecule beingunsaturated, or hydrogen, at least two R′ radicals per molecule beinghydrogen, and m has an average value in the range of about 10-1,500.Cyclic polydiorganosiloxanes analogous to those of the formula above mayalso be employed. The hydride silicone preferably is a hydrogenpolydimethylsiloxane.

[0023] The preferred number average molecular weight range for thehydride silicone is in the range of about 1,000-28,000, corresponding toa value of m in the range of about 13-380.

[0024] The polymers according to the invention are obtained from thesebinders by curing or cross-linking with suitable cross-linkers.

[0025] Polymer or oligomer:

[0026] Any fluid fluorinated alkyl- or alkoxy-containing polymer oroligomer is suitable.

[0027] Examples are:

[0028] a) Linear and trifluoromethyl branched fluorine end-cappedperfluoropolyethers (e.g., Fomblin Y®, Krytox K® fluids, or Demnum S®oils);

[0029] b) Linear di-organo (OH) end-capped perfluoropolyethers (e.g.,Fomblin Z DOL®, Fluorolink E®);

[0030] c) Low MW polychlorotrifluoroethylenes (e.g., Daifloil CTFE®fluids).

[0031] In all cases the fluorinated alkyl- or alkoxy-containing polymeror oligomer is not reactive towards the binder and does not take part inany cross-linking reaction. Other mono- and diorgano-functionalend-capped fluorinated alkyl- or alkoxy-containing polymers or oligomerscan also be used (e.g., carboxy-, ester-functional fluorinated alkyl- oralkoxy-containing polymers or oligomers).

[0032] Fillers:

[0033] Examples of fillers that can be used in the coating compositionaccording to the present invention are barium sulphate, calciumsulphate, calcium carbonate, silicas or silicates (such as talc,feldspar, and china clay), aluminium paste/flakes, bentonite or otherclays. Some fillers may have a thixotropic effect on the coatingcomposition. The proportion of fillers may be in the range of from 0 to25% by weight, based on the total weight of the coating composition.

[0034] Pigments:

[0035] Examples of pigments that can be used in the coating compositionaccording to the present invention are black iron oxide and titaniumdioxide. The proportion of pigments may be in the range of from 0 to 10%by weight, based on the total weight of the coating composition.

[0036] Catalysts:

[0037] Examples of catalysts that can be used include the carboxylicacid salts of various metals, such as tin, zinc, iron, lead, barium, andzirconium. The salts preferably are salts of long-chain carboxylicacids, for example dibutyltin dilaurate, dibutyltin dioctoate, ironstearate, tin (II) octoate, and lead octoate. Further examples ofsuitable catalysts include organobismuth and organotitanium compoundsand organo-phosphates such as bis(2-ethyl-hexyl) hydrogen phosphate.Other possible catalysts include chelates, for example dibutyltinacetoacetonate. Further, the catalyst may comprise a halogenated organicacid which has at least one halogen substituent on a carbon atom whichis in the α-position relative to the acid group and/or at least onehalogen substituent on a carbon atom which is in the β-position relativeto the acid group, or a derivative which is hydrolysable to form such anacid under the conditions of the condensation reaction.

[0038] Cross-linking:

[0039] The presence of a cross-linker for the resin is only necessary ifthe resin cannot be cured by condensation. This depends on thefunctional groups that are present in the resin. In general, when theresin comprises alkoxy groups, the presence of a cross-linker is notnecessary. If the resin comprises alkoxy-silyl groups, in general thepresence of a small amount of a condensation catalyst and water issufficient to achieve full cure of the coating after application. Forthese compositions, normally atmospheric moisture is sufficient toinduce curing, and as a rule it will not be necessary to heat thecoating composition after application.

[0040] The optionally present cross-linker can be a cross-linking agentcomprising a functional silane and/or one or more oxime groups. Examplesof such cross-linking agents are presented in WO99/33927. Mixtures ofdifferent cross-linkers can also be used.

[0041] Solvent:

[0042] The process for forming the curable polysiloxane- ornon-perfluoropolyether- containing polymer is most conveniently carriedout using a solution of the material in a non-reacting reacting volatilesolvent. Suitable solvents include aromatic hydrocarbons, alcohols,ketones, esters, and mixtures of the above with one another or analiphatic hydrocarbon. In order to minimise the use of solvent onenvironmental grounds, it is advantageous to use as concentrated asolution as possible which is compatible with the coating techniqueemployed. In principle, the maximum solids content may be as high as 90%by weight or even more, but in general the maximum practicable solidscontent will range from 70-80% by weight.

[0043] Application:

[0044] The coating composition can be applied by normal techniques, suchas brushing, roller coating, or spraying (airless and conventional). Toachieve proper adhesion to the substrate it is preferred to apply theanti/non-fouling coating composition to a primed substrate. The primercan be any conventional primer/sealer coating system. Good results werefound, in particular with respect to adhesion, when using a primer thatcomprises an acrylic siloxy-functional polymer, a solvent, a thixotropicagent, a filler, and, optionally, a moisture scavenger. Such a primer isdisclosed in WO 99/33927. It is also possible to apply the coatingcomposition according to the present invention on a substrate containingan aged anti-fouling coating layer. Before the coating compositionaccording to the present invention is applied to such an aged layer,this old layer is cleaned by high-pressure water washing to remove anyfouling. The primer disclosed in WO 99/33927 can be used as a tie coatbetween the aged coating layer and the coating composition according tothe present invention. After the coating has been cured, it can beimmersed immediately and gives immediate anti-fouling and foulingrelease protection. As indicated above, the coating compositionaccording to the present invention has very good anti-fouling andfouling release properties. This makes these coating compositions verysuitable for use as anti-fouling or non-fouling coatings for marineapplications. The coating can be used for both dynamic and staticstructures, such as boat hulls, buoys, drilling platforms, oilproduction rigs, and pipes which are immersed in water. The coating canbe applied on any substrate that is used for these structures, such asmetal, concrete, wood or fibre-reinforced resin.

[0045] The invention will be elucidated with reference to the followingexamples.

[0046] The kinematic viscosity of the fluids used in the examples can bedetermined according to the following method. The time is measured inseconds for a fixed volume of liquid to flow under gravity through thecapillary of a calibrated viscometer (such as an Ubbelohde viscometer)or the orifice of a flow cup under a reproducible driving head and at aclosely controlled temperature.

[0047] Such tests are described for example in Test Method D445-01Standard Test Method for Kinematic Viscosity of Transparent and OpaqueLiquids (the Calculation of Dynamic Viscosity), ISO 3104-IP 71-BS 2000-DIN 51550, and Test Method D5125-97 Standard Test Method for Viscosityof Paints and Related Materials by ISO Flow Cups. The kinematicviscosity is the product of the measured flow time and the calibrationconstant of the viscometer.

[0048] Kinematic viscosity is a measure of the resistance to gravityflow of a fluid, the pressure head being proportional to its density.Multiplying the kinematic viscosity with the density of the product at20° C. gives the dynamic viscosity.

EXAMPLE 1

[0049] A three-pack coating composition was prepared with theformulation:

[0050] Base

[0051] 33 g α, ω,-hydoxy-functional polydimethyl siloxane (dynamicviscosity 35 poise)

[0052] 3 g Daifloil #10® (a chlorotrifluoroethylene polymer, ex DaikinIndustries, kinematic viscosity 150 cST (measured in conformity with JISK 6893))

[0053] 5 g xylene

[0054] Curing agent

[0055] 1.7 g tetraethyl orthosilicate

[0056] 5 g xylene

[0057] Catalyst solution

[0058] 0.28 g dibutyltindilaurate

[0059] 2.54 g 2,4-pentanedione

EXAMPLE 2

[0060] A three-pack coating composition was prepared with theformulation:

[0061] Base

[0062] 33 g ,α,ω-hydroxy -functional polydimethyl siloxane (dynamicviscosity 35 poise)

[0063] 3 g Demnum S20® (a perfluoropolyether, ex Daikin Industries,kinematic viscosity 29 cSt (measured in conformity with ASTM D2270-86))

[0064] 5 g xylene

[0065] Curing agent

[0066] 1.7 g tetraethyl orthosilicate

[0067] 5 g xylene

[0068] Catalyst solution

[0069] 0.28 g dibutyltin dilaurate

[0070] 2.54 g 2,4-pentanedione

EXAMPLE 3

[0071] A three-pack coating composition was prepared with theformulation:

[0072] Base

[0073] 65 g α,ω-hydroxy-functional polydimethyl siloxane (dynamicviscosity 35 poise)

[0074] 9 g xylene

[0075] Curing agent

[0076] 3.0 g tetraethylorthosilicate

[0077] 8.0 g Fomblin Y-25® (a perfluorinated polyether, ex Ausimont,kinematic viscosity 250 cSt (measured in conformity with ASTM D445))

[0078] 9.5 g xylene

[0079] Catalyst solution

[0080] 0.5 g dibutyl tindilaurate

[0081] 4.8 g 2,4-pentanedione

EXAMPLE 4

[0082] A three-pack coating composition was prepared with theformulation:

[0083] Base

[0084] 65 g α, ω-hydroxy-functional polydimethyl siloxane (dynamicviscosity 35 poise)

[0085] 9 g xylene

[0086] Curing agent

[0087] 3.0 g tetraethyl orthosilicate

[0088] 3.0 g Fluorolink E® (a perfluorated polyether, ex Ausimont,kinematic viscosity 145 cSt (measured in conformity with ASTM D445))

[0089] 9.5 g xylene

[0090] Catalyst solution

[0091] 0.5 g dibutyltin dilaurate

[0092] 4.8 g 2,4-pentanedione

EXAMPLE 5

[0093] A two-pack coating composition was prepared with the formulation:

[0094] Base

[0095] 92 g m-polymer FR355® (silicone/acrylic hybrid polymer, exWacker) 5 g Fomblin m30® (a perfluorinated polyether, ex Ausimont,kinematic viscosity 280 cSt (measured in conformity with ASTM D445))

[0096] Curing agent

[0097] 2.8 g T914® catalyst/curing agent (ex Wacker)

EXAMPLE 6

[0098] A one-pack coating composition was prepared with the formulation:

[0099] 30.0 g acrylic siloxy-functional polymer (acrylic polymer Baccording to WO 99/33927, p. 29)

[0100] 3.0 g Fluorolink E® (a perfluorated polyether, ex Ausimont,kinematic viscosity 145 cSt (measured in conformity with ASTM D445))

[0101] 10.0 g trimethyl benzene

[0102] 0.5 g 2-ethylhexyl hydrogenphosphate

EXAMPLE 7

[0103] A two-pack coating composition was prepared with the formulation:

[0104] 100 g α,ω-hydroxy-functional polydimethyl siloxane (dynamicviscosity 35 poise)

[0105] 6 g Krytox K7® (a perfluoropolyether, ex DuPont, kinematicviscosity 8.3 cSt (measured in conformity with ASTM D445))

[0106] 3 g air floated silica (Aerosil®)

[0107] 10 g titanium dioxide (Tiona 472®)

[0108] 6 g methyl-tris(methylethylketoxime)silane

[0109] Catalyst solution

[0110] 15 g trimethyl benzene

[0111] 0.08 g dibutyltin dilaurate

EXAMPLE 8

[0112] A one-pack coating composition was prepared with the formulation:

[0113] 55 g α,ω(-hydroxy-functional functional polydimethyl siloxane(dynamic viscosity 35 poise)

[0114] 2.5 g methyltrimethoxy silane

[0115] 2.20 g air floated silica (Aerosil®)

[0116] 5 g titanium dioxide (Tiona 472®)

[0117] 2 g Demnum S200® (a perfluoropolyether, ex Daikin Industries,kinematic viscosity 203 cSt (measured in conformity with ASTM D2270-86))

[0118] 1.00 g titanium ethylacetoacetonate

[0119] 29.40 g trimethyl benzene

EXAMPLE 9

[0120] Anti-Fouling Testing

[0121] The compositions of Examples 3, 4, and 5 were applied by brushonto wood substrates primed with an anti-corrosive undercoat. For staticanti-fouling assessment the coated substrates were immersed in atropical marine environment known for its heavy hard-shelled andsoft-bodied animal fouling and a European marine estuary known for itsweed, slime, hard-bodied and soft-bodied animal fouling. After 3 monthsthe accumulated fouling was significantly less than that of controlsubstrates coated only with the anticorrosive primer, and less than thatof a standard substrate coated with a silicone coating not containing afluorinated fluid additive but maintained under the same conditions overthe same period of time. Any fouling on coatings of Examples 3-5 couldbe removed very easily by light rubbing, whereas accumulated fouling onthe control substrates could not be removed in a similar way.Quantitative fouling properties % Soft- % hard- Fouling % Slime % Weedbodied bodied % Total release Weeks Example fouling fouling foulingfouling fouling rating Immersed Immersed at tropical site 3 0 0 30 2 321 10 ST 0 0 23 11 34 1 10 CT 0 0 47 19 66 2 10 Immersed at estuary site3 23.2 0 1 18.3 42.5 1 13 ST 29 0 1.3 14.7 45 1 13 CT 12.5 0 11.7 43.367.5 4 13 Immersed at tropical site 4 0 0 23 3 26 N/A 14 ST 0 0 31 9 40N/A 14 CT 0 0 56 25 81 N/A 14 Immersed at tropical site 5 0 0.8 42.5 5598.3 1 11 ST 0 1.7 34.2 59.2 95 1 11 CT 0 3.3 13.3 79.2 95.8 1 11

1. An anti-fouling composition which comprises a cured or cross-linked polymer free of perfluoropolyether moieties and a fluid fluorinated alkyl- or alkoxy-containing polymer or oligomer.
 2. The anti-fouling composition of claim 1, wherein the fluorinated alkyl- or alkoxy-containing polymer or oligomer comprises a repeating unit of the general formula: —{[CFR—(CFR)_(m)—(O)_(n)]_(p)—[CFR—O]_(q)}— wherein n is 0 or 1, m is an integer from 0 to 4, R independently is H, F, Cl, Br, or CF₃, and the ratio q/p is 0-10.
 3. The anti-fouling composition of claim 2, wherein R is F or CF₃.
 4. The anti-fouling composition of claim 2, wherein the repeating unit is —[CF₂—CF₂—CF₂—O]— and/or —[CF(CF₃)—CF₂—O]—.
 5. The anti-fouling composition of claim 2, wherein the repeating unit has the formula —{[CF₂—CF₂—O]_(p)—[CF₂—O]_(q)}— and the ratio q/p is 1.25-2.0.
 6. The anti-fouling composition of claim 1, wherein the average-weight molecular weight of the fluorinated alkyl- or alkoxy-containing polymer or oligomer is 400-40,000.
 7. The anti-fouling composition of claim 1, wherein the cured or cross-linked polymer is an organosiloxane-containing polymer.
 8. The anti-fouling composition of claim 1, wherein the cured or cross-linked polymer comprises a repeating unit of the general structure —[SiR₁R₂—O]—, wherein R₁ and R₂ are independently hydrogen, alkyl, aryl, aralkyl, or a vinyl group.
 9. The anti-fouling composition of claim 8, wherein R₁ and R₂ are independently methyl or phenyl.
 10. The anti-fouling composition of claim 8, wherein R₁ and R₂ are methyl.
 11. A method for inhibiting fouling of a substrate in an aquatic environment by applying the anti-fouling composition of claim 1 to the substrate. 